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31.
KNUT STALSBERG EILIV LARSEN DAG OTTESEN HANS PETTER SEJRUP 《Boreas: An International Journal of Quaternary Research》2003,32(1):149-166
Glacial lineations on a bank area and a coastal lowland, both bordering the Norwegian Channel, are studied with regard to morphology and distribution by means of side-scan sonar data, detailed digital maps and fieldwork. Their genesis and age are further elucidated through stratigraphic and sedimentologic information from excavations in one typical coast-parallel drumlin. Four excavated sections revealed four lithologic units: Prodeltaic glaciomarine sand, glaciofluvial gravel, glaciomarine diamicton and deformation till. After Middle Weichselian delta progradation, glaciomarine diamicton was deposited and later subglacially reworked by a northwards flowing glacier. The two upper diamictons form the main volume of the ridge, which is interpreted as a drumlin, and imply a reinterpretation of the Jæren part of the so-called Lista moraine. Preconsolidation of glaciomarine diamicton suggests a maximum ice thickness of 500 m during drumlin formation, indicating an ice surface slope of 1 m/km. The occurrence of sediments that provided low basal shear stresses, and the orientation of drumlins and megaflutes indicating ice confluence both point to high glacier flow velocities and suggest that an ice stream, rather than a slower moving part of the ice sheet, occupied the Norwegian Channel during the Late Weichselian maximum. Deformation till overlying, more or less, undeformed glaciomarine diamicton suggests that high glacier velocities during periods of low driving stresses were possible due to a subglacial deformable layer. 相似文献
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33.
GUNNAR LARSEN 《Boreas: An International Journal of Quaternary Research》1987,16(4):405-410
Applied geology has broad terms of reference in the Danish Quaternary. Environmental geology, which is one aspect of this, can be defined as the contribution which geology can make to improve the quality of life. Nature conservation is an important aspect of environmental geology. Geologisk Institut, Aarhus University, has been involved for several years with the conservation of a variety of sites, including Quaternary profiles and landscapes. The work has been carried out in co-operation with, among others, Fredningsstyrelsen under the Ministry of the Environment and the county council authorities. This article presents examples of this activity, including topics of national, as well as of regional and more local importance. 相似文献
34.
JAN MANGERUD STEINAR GULLIKSEN EILIV LARSEN ODDVAR LONGVA GIFFORD H. MILLER HANS-PETTER SEJRUP EIVIND SØNSTEGAARD 《Boreas: An International Journal of Quaternary Research》1981,10(4):447-462.
Seven localities with fossil-bearing tills were found in the Ålesund area. Fifteen radiocarbon dates of marine shells in the tills all gave ages between 28,000 and 38,000 years B.P. In spite of a general scepticism to shell dates giving high finite ages, these ages may be accepted mainly because of the quality of the shells, the geological situation in which they were found, and identical results for different fractions. The ice-free period is named the Ålesund Interstadial. and its Middle Weichselian age is also suggested by amino acid D/L ratios in shells, compared with Late Weichselian and Eemian ratios. Shell and foraminifera faunas suggest arctic conditions with the Atlantic water present during the optimal period. The tills are non-sorted, compacted and interpreted to be basal tills. Their age is bracketed between c. 28,000 and 12,800 years B.P. 相似文献
35.
The stratigraphy in Hamnsundhelleren is as follows. A basal weathered rock bed of unknown age is followed by laminated clay deposited under stadial conditions and correlated with palaeomagnetism to the Laschamp excursion (43–47 000 yr BP). Angular blocks, bones and clay above this are 14C dated to the Ålesund Interstadial (28–38 000 yr BP). Another stadial laminated clay following the Ålesund Interstadial includes a palaeomagnetic excursion correlated with Lake Mungo (28 000 yr BP). The newly discovered Hamnsund Interstadial above this consists of frost-weathered clay and scattered angular blocks. It is 14C dated to 24 500 yr BP on bones mixed into the Ålesund Interstadial. The Hamnsund Interstadial is succeeded by another stadial laminated clay and then a Late-glacial–Holocene mixture of bones and blocks. In Hamnsundhelleren and other similar caves four successive phases of sedimentary environments for each ice-free–ice-covered cycle have been identified: (i) ice-free phase (deposition of bones and frost-weathered blocks); (ii) subaerial ice-dammed lake phase (sand or silt deposited in a lateral glacial lake); (iii) subglacial ice-dammed lake phase (cave closed by ice, deposition of till, debris flows and laminated clay); (d) ice-plugged phase (cave is plugged by frozen lake water and/or glacial ice, no deposition). 相似文献
36.
FITTON J. G.; LARSEN L. M.; SAUNDERS A. D.; HARDARSON B. S.; KEMPTON P. D. 《Journal of Petrology》2000,41(7):951-966
Drilling along a 63°N transect off SE Greenland during OceanDrilling Program (ODP) Legs 152 and 163 recovered a successionof volcanic rocks representing all stages in the break-up ofthe volcanic rifted margin. The rocks range from pre-break-upcontinental tholeiitic flood basalt, through syn-break-up picrite,to truly oceanic basalt forming the main part of the seaward-dippingreflector sequence (SDRS). All the lava flows recovered fromthe transect were erupted in a subaerial environment. 40Ar–39Ardating shows that the earliest magmas were erupted at 相似文献
37.
ASTRID LYSÅ MARIA A. JENSEN EILIV LARSEN OLA FREDIN IGOR N. DEMIDOV 《Boreas: An International Journal of Quaternary Research》2011,40(3):481-497
Lyså, A., Jensen, M. A., Larsen, E., Fredin, O. & Demidov, I. N.* 2010: Ice‐distal landscape and sediment signatures evidencing damming and drainage of large pro‐glacial lakes, northwest Russia. Boreas, Vol. 40, pp. 481–497. 10.1111/j.1502‐3885.2010.00197.x. ISSN 0300‐9483. Sediments from river sections and the morphology of the upper reaches of Severnaya Dvina and Vychegda in northwest Russia show evidence of the existence of large ice‐dammed lakes in the area twice during the Weichselian. During the Late Weichselian, three separate ice‐dammed lakes (LGM lake(s)) existed, the largest one at about 135 m a.s.l. having a volume of about 1510 km3. Stepwise and rapid lake drainage is suggested to have taken place within less than 1000 years. The locations of various passpoints controlled the drainage, and when the lake was at its maximum level water spilled southeastwards into the Volga basin. Later, but before the lake water finally drained into the White Sea, water was routed northeastwards into the southeastern part of the Barents Sea. The oldest lake, the White Sea lake, existed around 67–57 ka ago, slightly in conflict with earlier palaeogeographic reconstructions regarding the chronology. The extent of the lake was constrained by, in addition to the Barents Sea ice‐sheet margin in the north, thresholds in the drainage basin. Later, one threshold was eroded and lowered during the LGM lake drainage. Given a lake level of about 115 m a.s.l., a lake area of about 2.5 × 104 km3 and a water volume of about 4800 km3, the lake drainage northwards and into the ocean probably impacted the ocean circulation. 相似文献
38.
KAREN LUISE KNUDSEN PETER KRISTENSEN NICOLAJ KROG LARSEN 《Boreas: An International Journal of Quaternary Research》2009,38(4):787-810
The marine Quaternary of Vendsyssel has been studied in a series of new boreholes in the area, and the climatic development is discussed on the basis of foraminiferal assemblages and stable isotopes. The foraminiferal zones are correlated with previously published records from northern Denmark, and the spatial local and regional distribution is discussed in details based on the new evidence. The new data show that the marine sedimentation in Vendsyssel was not continuous from the Late Saalian to the Middle Weichselian, as previously thought. For example, there is indication of a hiatus at our key site, Åsted Vest in the central part of Vendsyssel, at the transition between regional foraminiferal zones N4 and N3, i.e. at the Late Saalian (MIS 6) – Eemian (MIS 5e) transition. The hitherto most complete Early Weichselian succession (zone N2) in Vendsyssel is presented from Åsted Vest. Deposits from the Early Weichselian sea‐level lowstands (MIS 5d and 5b) may, however, be missing in parts of the area. Two major breaks in the marine deposition during the Middle Weichselian represent glacial advances into northern Denmark. The first event occurred just after deposition of the regional foraminiferal zone N2 (late MIS 4), and the second event in the middle part of zone N1 (early MIS 3). Zone N1 is succeeded by a series of non‐marine units deposited during the sea‐level lowstand of the Weichselian maximum glaciation (late MIS 3 and MIS 2), including deeply incised tunnel valleys, which have been refilled with non‐marine sediments during the Late Weichselian. Vendsyssel was inundated by the sea again during the Late Weichselian, at c. 18 kyr BP. Subsequently, the marine conditions were gradually changed by forced regression caused by local isostatic uplift, and around the Weichselian–Holocene transition most of Vendsyssel was above sea level. A continuous deposition across the Late Weichselian–Holocene boundary only occurred at relatively deep sites such as Skagen. The environmental and climatic indications for Vendsyssel are in accordance with the global sea‐level curve, and the Quaternary record is correlated with the oxygen isotope record from the NorthGRIP ice core, as well as the marine isotope stages. 相似文献
39.
HANS PETTER SEJRUP MARIANNE IVERSEN EILIV LARSEN JON Y. LANDVIK JURAJ JANOCKO 《Boreas: An International Journal of Quaternary Research》1999,28(2):326-346
Foraminiferal biostratigraphy, stable isotopes and amino-acid diagenesis have been investigated in a 125 m (+ 1 to — 124 m a.s.l.) long core from Jæren, southwestern Norway. Two marine units, the 42 m thick Grødeland Sand and the 8 m thick Sunde Sand, were found between till beds. Based on the biostratigraphic data, nine foraminiferal assemblage zones are defined. The Grødeland Sand shows a development from an ice-proximal glacial environment in the lower part, through an arctic, possibly shallow-water, environment, into a full interglacial open-shelf regime (the Grødeland Interglacial). The Grødeland Interglacial sediments (zone 6 Cassidulina laevigata-Cibicides zone) were deposited at a water depth of 20 m, in an open, high-energy shelf environment with temperature conditions similar to those prevailing in the northern North Sea today. The interglacial sediments are followed by deposits characteristic of an arctic environment which become more ice proximal upwards. Superimposed on the Grødeland Sand is a diamicton interpreted as till. Above the till is the upper marine unit (the Sunde Sand), which in the lower part yielded a shallow-water arctic fauna replaced upwards by an ice-proximal facies. The upper part of the Sunde Sand is barren of foraminifera and is superimposed by an upper till. The Sunde Interstadial is defined as a climatostratigraphic event resulting in deglaciation of western Norway and deposition of the Sunde Sand. Based on amino acid geochronology and inferences from the biostratigraphy, the Grødeland Interglacial is assigned to oxygen-isotope stage 7, whereas the Sunde Interstadial is assigned to the Early Weichselian. Combined with existing data from the North Sea region and the Norwegian Sea, it is concluded that for stage 7, in addition to stages 1 and 5e, there must have been a strong influx of Atlantic water into the Norwegian Sea north of the British Isles. This circulation created a similar north-south gradient in water masses in the North Sea to that which occurred during the Eemian and the Holocene. In the Nordic Seas, however, the stage 7 warm influx was probably restricted to the eastern part of the basin, unlike the later warm periods. This led to the development of fully interglacial conditions in the North Sea region, even though the palaeoceanographic data from the central part of the Nordic Seas suggest relatively cooler conditions for oxygen-isotope stage 7. 相似文献
40.
KURT H. KJæR EILIV LARSEN SVEND FUNDER IGOR N. DEMIDOV MARIA JENSEN LENA HAKANSSON REW MURRAY 《Boreas: An International Journal of Quaternary Research》2006,35(3):444-475
Sediment successions from the Kanin Peninsula and Chyoshskaya Bay in northwestern Russia contain information on the marginal behaviour of all major ice sheets centred in Scandinavia, the Barents Sea and the Kara Sea during the Eemian-Weichselian. Extensive luminescence dating of regional lithostratigraphical units, supported by biostratigraphical evidence, identifies four major ice advances at 100-90, 70-65, 55-45 and 20-18 kyr ago interbedded with lacustrine, glaciolacustrine and marine sediments. The widespread occurrence of marine tidal sediments deposited c. 65-60 kyr ago allows a stratigraphical division of the Middle Weichselian Barents Sea and Kara Sea ice sheets into two shelf-based glaciations separated by almost complete deglaciation. The first ice dispersal centre was in the Barents Sea and thereafter in the Kara Sea. It is possible to extract both flow patterns from ice marginal landforms inside the southward termination. Accordingly, it is proposed that the Markhida line and its western continuation are asynchronous and originate from two separate glaciations before and after the marine transgression. The marine sedimentation occurred during a eustatic sea-level rise of up to 20 m/1000 yr, i.e. the Mezen Transgression. We speculate that the rapid eustatic sea-level rise triggered a collapse of the Barents Sea Ice Sheet at the MIS (Marine Isotope Stage) 4 to 3 transition. This is motivated by lack of an early marine highstand, the timing of events, and the marginal position of Arkhangelsk relative to open marine conditions. 相似文献